feat(demo): real registry UIs, IndeeHub iframe proxy, mempool tab, media Range

- App UIs now use the real registry shells with dummy data: bitcoin-ui for
  Bitcoin Core (Satoshi subversion) and Bitcoin Knots (Knots subversion) via
  per-path /app/bitcoin-{core,knots}/bitcoin-status; the real lnd-ui (mock
  /proxy/lnd/v1/getinfo+channels, /lnd-connect-info, /api/container/logs); the
  static fedimint-ui. ElectrumX already on the real electrs-ui. Custom mock UIs
  dropped — accurate UX.
- IndeeHub loads in the iframe: nginx reverse-proxies /app/indeedhub/ →
  indee.tx1138.com and strips X-Frame-Options/CSP (it blocked framing before).
- Mempool opens in a new tab (mempool.space can't be iframed).
- Cloud media playback: HTTP Range support in the curated-file server so audio/
  video can stream and seek (needs real files dropped into demo/files/).
- Dockerfile/.dockerignore copy docker/lnd-ui + docker/fedimint-ui.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.dockerignore

@@ -12,6 +12,8 @@
 docker/*
 !docker/bitcoin-ui/
 !docker/electrs-ui/
+!docker/lnd-ui/
+!docker/fedimint-ui/
 
 # Allow backend source for ISO source builds
 !core/